text:
How do I keep my home address private following new aircraft registration?
I'm looking at filing out an 8050-1 for a new airplane in the US and the FAA is asking me for my name, and address. My concern is that once I register these bits of information, specifically my home address, become publicly available. So I'm wondering is there anyway of registering an aircraft tag in a way that keeps that information private? Are there any proxy registration services that exist for this purpose?

Don't you already have this problem of your address being publicly available with your pilots certificate? Assuming you have one. I share your concern, but I think it's impossible to avoid in the modern age.

what do you have to hide from the FAA that you don't want them to have your name and address?

The address info for your pilot certificate does NOT have to be available to the public... You can opt to have it not published. Your name & ratings still show up when searching the FAA records, but your address does not. Don't know if this option is available for other things, i.e. aircraft registration.

@jwenting I think his point isn't about the FAA having his address, it's that aircraft owners' addresses are public information, so anyone can search the N number and find his home address.

I was looking through this site and several just list a po box. Most of them are corporations, but the plane the link leads to is an individual with just a po box

@Pondlife ok, weird. Privacy law here would never allow that.

The 'usual' alternative is to have the aircraft owned by a legal entity like an LLC or trust of some kind (trusts are also used by foreigners who own N-reg aircraft). But that only adds a layer of obfuscation: if someone really wants to know who owns the aircraft then they can dig into the LLC or trust ownership details. That information is usually also public although it's at the state level not federal level.
The best thing here is to talk to an attorney in your state, preferably one with aviation experience. He can tell you what legal entities might fit your needs, as well as the pros, cons and costs of each one.

Talking to an attorney, thanks for the initial idea!

Some states do not publish or share LLC owner info.  Wyoming and Nevada come to mind.

There are several ways to have an address that isn't your house.
Private mail box

"Arizona" Joe Flyer
24 W Camelback Road #9999
  Phoenix AZ 85013

This is a privately managed version of the PO Box with a number of enhancements. The address looks like a street address, so most askers who won't accept a mailbox will accept a PMB. The PMB staff can forward your mail to you anytime or at intervals, tell you if you have mail if you call, and even call you if something comes in.  They can also accept from any carrier (even Amazon) and forward via any carrier.   It is maybe twice the cost of a PO box.
You must give it a real address.  It is state licensed so it will answer any subpoena.
LLC

Delaware-Chesapeake Bay Flyers LLC
905 Broadway St. #9999
  Sheridan Wyoming 82801

Having an LLC own a plane makes so much sense for other reasons - not least, reducing the considerable liability of your plane crashing into something valuable.   With individual ownership that liability is bottomless.  With LLC or corporate structure, the LLC goes bankrupt and you're in the clear.  This arrests your liability as the plane's owner, but not your liability as its pilot.
Taxwise, if you're the only member, the IRS calls it a "disregarded entity" and counts it as if it's part of you (e.g. a proprietorship).
LLCs have members and managers.  Members own, managers control. There are some useful liability-containment tricks possible with this.
States register LLCs.  Most states will cheerfully hand owner the addresses of the LLC members, though most will allow PO boxes and PMBs.  Some states shield/conceal the LLC member addresses from casual inquiry, notably Wyoming and Nevada. My undertanding is they also put up roadblocks to legal inquiry, refusing to answer subpoenas from other states, forcing the suer to re-sue in their state or Federal court.
Annual cost is

typically 20 dollar annual registration in your home state (lots more in CA or MA)
if you don't staff a physical location 9-5, then a Registered Agent in your home state ($50-300/year) - his duty is to accept service of lawsuits, hence the need to be open during business hours. If you already have a lawyer with an office, he'll do.
if registered out of state, business license there
if registered out of state, a Registered Agent in that state

This answer doesn't show relevant research. You cannot use a PO Box without providing a physical address. This is made clear on the form. Additionally, there is the requirement to provide the physical address of flight records for non-citizen corporations, due to limitations on foreign flight times that incurs.

No, the issue is the FAA requires a street address. My objection is that it appears you gave a generic "how do I hide my street address" answer that does not address the specific FAA requirements.

@user71659 okay then... That's not an uncommon issue, and a big selling point for PMBs...

"With individual ownership that liability is bottomless. With LLC or corporate structure, the LLC goes bankrupt and you're in the clear."  Check with a lawyer on that.  In some locales, an LLC that is wholly owned by a single owner does not provide liability protection.  I.e. it is as if the LLC did not exist.  Look under Single Member LLCs and Asset Protection for example.  More generally, the owner is still liable for the owner's personal actions.  In a sham LLC, only the owner can act.

LLCs are 500 dollars in MA, plus 20 dollar expediting fee, which you can't avoid, there are no paper forms you can send in that I can find; annual reports must be done online.

@CrossRoads probably same issue as CA.  Edited.


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Do any aircraft out there use negative lift?
I think negative lift is where high pressure forms on the top of the wing instead of the bottom. I know that Indy cars use negative lift and some sports cars do, but do any aircraft exist that use negative lift and why do they use negative lift?

Related: Do any airplane designs exist that don't involve a flight surface that provides downforce?

Short Answer: Yes
Long Answer: Well, partially....You see, lift is generated not only at the wings but also at the tail. The aircraft's tail has an elevator and a rudder (most single engine planes) by way of control structures. The pitching motion of the airplane is caused by altering the elevator's shape. The nose stays where it is (in the vertical plane) when the lift at the wings is balanced by that at the tail. However, when the lift at the tail increases the nose starts dropping. Similarly, when the lift at the tail decreases, the nose rises up. You could call the increased downward at the tail 'negative-lift'.
I hope that answered your question. If you are patient enough, try reading this chapter from the Pilot's Handbook of Aeronautical Knowledge. It is the same book I used for my pilot's license.

Thank You. Again, I appreciate the edit. I do not think I need to roll it back. I got a little help notification box here. That should help me format things better.

A lot of aircraft generate negative lift- not in the wings, but in the tail plane. This is used for stability. Consider a trimmed aircraft as shown below:

Image from grc.nasa.gov
On most aircraft, the center of gravity (through which weight acts) of the airplane is located near the center of pressure (through which lift acts) of the wing. If the center of presure of the wing is aft of the center of gravity, its lift produces a counter-clockwise rotation about the cg. A positive lift force from the tail produces a counter-clockwise rotation about the cg.
To trim the aircraft (i.e. no rotation about c.g), it is necessary to balance the torques produced by the wing and the tail. But since both rotations are counter-clockwise, it is impossible to balance the two rotations to produce no rotation. However, if the tail lift is negative it then produces a clockwise rotation about the cg which can balance the wing rotation. For this reason, the tailplane is designed to produce a negative lift.
Text from Trimmed aircraft- slightly modified.

so, why are the wings so far behind the center of gravity?

@njzk2 For longitudinal static stability. In short: if the aircraft's angle of attack increases (and/or its airspeed decreases,) the negative lift of the tail plane will decrease in magnitude (become less negative,) which will cause the pitching moments to become unbalanced, and the nose to drop. The nose dropping will, in turn, reduce the angle of attack and increase the airspeed, moving the aircraft back towards its previous attitude.

@njzk2 Similarly, if the airspeed increases and/or the AoA decreases, the tail plane's lift will become more negative, pushing the tail down and the nose up in order to move back toward the aircraft's previous attitude. Note that all of this occurs with no pilot (or autopilot) input. It's designed to be a mechanical property of the airframe itself.

Yes  .  .  .  .  .  .  .  .  .

"A good landing effort, Tony, but perhaps a little less flare next time?"

'Tis not quite a negative lift, when seen from the ground...

@yo' the plane can do that the right way up too to lose altitude, but this way is more obvious.

Imma say the pole holder on the far side is smarter than the pole holder on the near side.If the pilot's a little off on his aim, one gets a broken wrist, the other a broken face...

As the saying goes, a picture says a thousand words.

@reirab And half of them are "HONDA"

Yes. Most airplanes have the centre of mass forward of the centre of lift of the main wing(s). This would make the airplane "tip over" forwards, so the tailplane is an upside-down wing, and provides negative lift sufficient to balance the airplane. This is a conventional arrangement. On some, the "car spoiler" shape of the tailplane, with the flat side on top and the cambered side underneath, is very obvious.

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text:
Why does carburetor icing require manual attention by the pilot?
Why is it carburetor icing has to be handled manually by the pilot, at least in a helicopter? I am hoping very soon to take my PL/H lessons, I have a little understanding of mechanics and how things work and this is one subject that puts the willies up me as a potential student helicopter pilot. Why can it not be an automatic response built into the engine? After all, this is the 21st century.
Also, I am assuming every motorized engine is the same, so why does a helicopter require a manual response to carb icing but a motor vehicle doesn't? Do we not notice it because the vehicle is on the ground?

Perhaps because most IC engines used in aviation were actually designed in the 1950s?  AFAIK, few if any automobile engines used carburetors after about 1990.  I think most carbureted engines dealt with the problem mainly by circulating engine coolant under the carburetor, so it operated at a higher temperature.

@jamesqf Once upon a time, I ran a 1983 VW Golf 1.8L. As you say, the carb had a water circuit from the engine around it, controlled by a thermostat similar to that of the radiator, but in reverse: it opened water supply when the temperature was low enough in order to heat up the carb body. This Pierburg carb was already on the 1976 vintage Golf 1.6L.

The R22 and R44 have mechanical interconnects between the collective position and the carb heat. As you lower the collective, the interconnect raises the carb heat, and vice versa. Voila, auto carb heat.

This asks not about aircraft, but why cars don't suffer from carb ice. The answer seems to support that. Off topic.

This may be the 21st century, but a very large part of the light GA aircraft and engines in service today date from the 20th :-)

@rbp  Only some R22s have this.  I've probably flown about 15 different aircraft and none of them had any automatic assistance.  Never flown a 44 so don't know about those.

The point, simon, is that there is a fix, and you've even flown an aircraft that has the fix.  Also, I would be very interested to see the list of 15 different certificated piston, carbureted helicopters.

Not every motorized engine is the same: For example, you would be hard-pressed to find a carbureted car these days.
The most similar kind of land-vehicle engine you'll find would be a motorcycle engine, and those do in fact suffer from carburetor ice:
- A discussion of carb icing on the Ninja 250
- A thread about carb ice on Bike Talk Forums
Older cars with carburetors were also susceptible to carburetor ice, and eventually included measures to avoid or mitigate it.
This could include passive changes such as mounting the carburetor in a warm part of the engine compartment (usually above the block, in a downdraft configuration), semi-active changes like "heat risers" which would feed warm air into the intake (usually behind the throttle plate, but occasionally in front of it), or fully-active systems like automatic "heat flaps" and "Time/Temperature switches" which do the same thing as the carburetor heat control in an airplane but without the driver's input or control.
These systems aren't usually fitted to aircraft as they add both weight and complexity, and can come with their own disadvantages (such as reduced power if the carburetor heat flap is in the "on" (heating) position during takeoff or on a go-around).

So why don't we hear about ground vehicles suffering from carburetor ice as much? Three main reasons:

Carburetor ice is most likely to form at low power settings.
Your car or motorcycle probably doesn't spend much time at or near idle power unless you're stuck in traffic: A few seconds coasting to a stop and then you accelerate away again.
Carburetor ice is less dangerous when you're on the ground.
One of the most common times you'll have a carburetor ice problem is during an approach/landing, with the engine at or near idle power for an extended period of time (this is why many aircraft call for carb heat during landing). Having your engine die at this point is a pretty serious problem, especially if you need to execute a go-around.
The analog in a car or motorcycle is having your engine stall after spending an extended period idling (standing or stopped in traffic). Having your engine die when you try to accelerate away is inconvenient and will probably make other drivers honk their horns at you and say unkind things, but it's unlikely to kill you.
There's nothing the driver can do about it.
A driver doesn't usually have a "carburetor heat" handle to pull (except possibly in very old cars), so you can't turn around and say "Your engine stalled because you didn't do this." On top of that because the problem is usually more inconvenient than dangerous on the ground it's not likely to make news: "Driver had to sit on shoulder for 30 minutes while their carburetor thawed out. Hundreds inconvenienced by rubbernecking traffic." is simply not as newsworthy as "Airplane crashed!"

"A few seconds coasting to a stop and then you accelerate away again"  and "more inconvenient that dangerous" - not always!! I had carb icing in a car in the UK a few times back in the 1980s. The usual result was that the throttle was locked into position by the ice, so (1) the car didn't slow down when easing off the gas, and (2) putting the car out of gear with the throttle locked half-way down over-revved the engine until it cut out. (Simultaneously switching off the ignition without locking the steering, while not hitting the car in front, seemed like it was to complicated to attempt).

Re point #1, hereabouts (Sierra Nevada), it's quite usual to be at idle power for half an hour or so when descending a grade.

Now I know why some motorcycle riders rev their engine when stopped at a light.  They're preventing carb icing.

Cars can in theory suffer from this if humidity is high enough.
For what its worth not all planes are carbureted. A solid chunk of airplanes use fuel injection (mechanical) and FADEC control is quickly becoming popular. This eliminates the carb ice problem by eliminating the carb all together. Keep in mind that any system needs to be certified for the FAA. There is little reason for a company to spend money developing an anti ice carb system and have it certified when carbs are slowly going away and the ones we still service were certified years ago ("if it ain't broke don't fix it").
For what its worth it seems that there are sensor systems out there for it however I have never used one so I will hold back from commenting on how well they work.

I don't understand what FADEC has to do with carb ice. Fuel injection is the remedy.

Everyone is making the answer more complicated than it needs to be. The manufacturers can't build an automated carburetor deicing system for more than they could sell it for. Therefore, it's a manually actuated system.

It is because there is no reliable sensor that can detect when and how much ice is or could be present.
If there was some kind of super sensor that could tell if ice was forming in the throat of the carb, then maybe you could have a little computer and a solenoid that would actuate the carb heat, but this would require a lot of development and added complexity that has not been done yet. Also, what if the computer screwed up for some reason and your carb froze?
Another option would be to have the system automatically turn on the heat any time humidity and temperature reached certain levels. The problem with this is that if either of those (added) sensors failed then you could get iced. Also, the helicopter would be flying inefficiently constantly and burning excess fuel.

You're looking at the problem the wrong way round. The objective is not to detect ice. The objective is to prevent ice formation. If you can detect ice it is already too late. Ice formation is governed by three things, presence of moisture, air pressure and temperature. All three can be measured, but moisture and pressure sensors can be fouled by ice. So you measure temperature and you keep the system warm.

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text:
Why is this VDP not authorized?
I have to admit that I’ve always kind of struggled with the Visual Descent Point (VDP) concept. Looking at the Terminal Instrument Procedures (TERPS) definition:

“The VDP is a defined point on the final approach course of a
  non-precision straight-in approach procedure from which normal descent
  from the MDA to the runway touchdown point may be commenced, provided
  visual reference is established.”

Fine, I take that to mean that if I start down from Minimum Descent Altitude  (MDA) too far after passing the VDP then my descent won’t be “normal”. What I don’t get is when the VDP is “Not Authorized”. Take a look at the RNAV (GPS) Z RWY 24 approach for KTTN. Included in the notes is the statement: “VDP NA with Northeast Philadelphia altimeter setting”.

What does that mean? Why is the VDP not authorized now that the MDA is 60 feet higher? If I didn’t want to descend too late before, I certainly don’t want to go past the VDP when I’m 60 feet higher! Is the note just telling me I better have the required visual references in sight so I can start down BEFORE the VDP? That might not be possible if visibility is at the 1 mile minimum.
@voretaq7:
I understand the implications of altimeter setting from a different airport and how your actual altitude could be higher than indicated.
I guess I'm hung up on what it means to "use" the VDP. Assuming that you use the Dive-n-Drive technique (rather than a constant descent rate), then your statement "Fly the approach until you have the runway environment in sight and then figure out your own glide path intercept based on the visual references you have" is what you are going to do regardless of what altimeter setting you use. In that case, what does it mean to "use" the VDP? In a light piston aircraft with airspeed under control, I may prefer to wait until the VDP and make a steeper than normal descent even if my actual altitude if higher than indicated. That way, in poor visibility, I avoid obstacles that may exist below the MDA prior to the VDP. So exactly what is the FAA saying I'm not authorized to do while using the PNE altimeter setting?

You can always calculate (and then use) your own VDP; with the MDA being 60' higher than before, the new VDP would be about 0.2 NM further out. The chart is just saying that you can't use the published VDP if your MDA doesn't match the published MDA.

But, what does "use" the VDP mean? Is the FAA not saying I'm not authorized to wait until the published VDP to descend below MDA if I have the PNE altimeter setting? So I MUST descend before the published VDP? Exactly what action is "Not Authorized"?

It just means, don't use what's printed on the chart as authoritative.  It isn't telling you that you must descend before or that you can only descend after or anything like that.  It's just saying, don't blindly rely on the printed "1.2 DME" value, because that only works for the 620' MDA.  If you back up your visual references with a VDP that you calculated (probably about 1.4 DME at the higher MDA), that's fine, and it's always your option. What you aren't using is their # -- not that you're disallowed from using an appropriately calculated VDP.

That makes perfect sense and I'd be happy with your answer if "NA" in the notes meant "Not Applicable". But, as far as I know, it means "Not Authorized". The FAA is usually not wishy-washy when it comes to what's Authorized or not when it comes to IAPs. Hence, my confusion about why I wouldn't be Authorized to "use" (descend from) the VDP in this case.

I'd simply say that what isn't authorized for use is the number on the chart. If an examiner asks why you descended when you did & you answer "at 1.2 DME because that's the published VDP" (when you're on the PNE altimeter), that's bad. But the answer "at 1.4 DME because the 620 MDA + 60' adjustment - 193' TDZE, along with a 3 degree path gives me a VDP of 1.4 DME to the runway" should be just fine.

I agree and guess my gripe is really with the FAA's choice of wording. Another answer to the examiner could be: "We're in an IFR-equipped Super Cub with STOL kit and the ~4.1 degree descent from the 1.2nm VDP is well within its capabilities and my authority as PIC." But, since the VDP is "Not Authorized", could I be failed or violated?

Maybe safer to just say, "looked like a normal STOL approach to me, sir" and leave the "not authorized" 1.2 number out of the discussion.  I agree, the FAA's choice of wording OFTEN leaves a lot to be desired!

I think "how do I use a VDP?" would make a good separate question, since the original one has an answer now :)

The key is in the part of the procedure description I've highlighted:

When local altimeter setting not received use Northeast Philadelphia altimeter setting -- you're using the altimeter setting for an airport 15 miles away.
15 miles may not seem like a lot of distance, but it's enough for there to be a notceable variation in altimeter settings. The FAA assumes this error will be in the least favorable direction (i.e. your altimeter will indicate you're higher than you really are), and accordingly they take some precautions when you're using another field's altimeter setting.
In this particular case:

The decision altitudes (DAs) are higher.
Baro-VNAV (vertical guidance for your descent based on your altimeter) is not authorized.
The use of the charted Visual Descent Point (VDP) is not authorized.

The VDP is telling you "If you are on the approach path and remain at the MDA until over this point on the ground you'll be on the glide path to the runway" (or alternatively "You can plan a constant-rate descent that intersects the MDA over this point and you'll be on the glide path to the runway").
Using the charted VDP is specifically not authorized in this case because the nominal descent angle you will have passing through it counts on your altimeter being accurate and your aircraft being at the MDA. Since the MDA has changed and we're using a remote altimeter setting the location of the VDP isn't going to be what's shown on the chart. (For example, if you're 60 feet higher than you "should" be & everything else is perfect the VDP moves further away from the airport to provide the same glide path at a higher altitude).
Rather than charting several visual descent points (which would be futile anyway as you can't know the altimeter error portion of the equation) the FAA just says "Don't use it: Fly the approach until you have the runway environment in sight and then figure out your own glide path intercept based on the visual references you have."

Please see edit to my original post. It was too long to add as a comment to your answer.

Even with the local altimeter setting, an altimeter can still be 75' off & still be with tolerance, so altimetery errors are always a bit of an unknown.  A VDP ensures that you're in the right ballpark to start your descent, and not biting off on illusory visual cues too soon or waiting until unsafely steep to start the descent. The salient point is the effect of the higher MDA on the VDP, which was nicely explained. Pilots always have the option to back up visual references with a calculated VDP (even if none is published) -- just don't rely on one calculated for a different MDA!

@GregValvo I tweaked the answer a little to clarify some bits, but like egid said you may want to ask a separate "How do you use a VDP?" question where we can go into a lot more detail (calculated vs. charted for starters). The short answer is you're kind of always "using a VDP" to some extent: when you have the runway in sight at the MDA & fly along until the PAPI lights say you've intercepted the glide path that's "the visual descent point". You just might not be using the one on the cart that the FAA calculated for you.


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What exactly happens when I try to maintain the flare when coming to a hover?
I've been considering this question.  I believe myself to be an average pilot but I'm embarrassed to say that I could not figure out the answer to the following question:
I flare and use power to maintain height, for example coming into the hover.  As I slow, I must keep increasing power.  I have enough power to hover out of ground effect.
If I attempt to continue maintaining the flare, attempting to come to a stop, I will sink and if I don't do anything about it, I will hit the ground. Why?
I've been trying to think through all of the key aerodynamic effects but keep hitting a brick wall.
P.S.  Fixed wing pilots - if you don't have a good understanding of helicopters, please try to resist the temptation to guess.  A helicopter in this flight regime is similar to a fixed wing in that it's a powered, heavier than air flying machine. End of list.

@mins.  I mean continue to maintain the flare attitude, i.e. nose pitch up.  I've edited the question.  Imagine holding pitch up and attempting to come to zero airspeed.  Of course, it won't work.  I'm trying to figure out why.

I don't think this is correct Simon. This may be due to your description, which I'm finding difficult to follow. Possibly by your description of maintaining the flare. You should just find you come to a stop in the hover, as mins pointed out. What are you trying to do in order to keep the nose up at that point?

@Rory.  I'm not trying to do anything.  I know perfectly well how to come to a hover (otherwise, I wouldn't be a pilot would I?).  Are you a rotary pilot?  If I try to keep back pressure on the cyclic to maintain nose pitch up, what happens and why?  Of course, I am never going to test this out (well, maybe at 1500ft with a CFI beside me).

@mins, that's the problem.  I don't know :) At the end of a quick stop, or coming to the hover, we level the pitch and checkup on the collective. I've just never questioned that, it's what we do! But what would happen if I used cyclic to maintain the nose pitch up (say 30 degrees) and collective to maintain height.  I know I'll hit the ground.  But what happens and why?  So between let's say 10 kts after loss of translational lift and coming to 0 kts.  That won't stress the blades and I'm not flying into my own downwash, although I guess there is some recirculation at the rear of the disc.

Simon - watch the second video on my answer. A beautiful example of doing it right - while very scary for spectators:-)

Am I the only one that finds this question by a licensed pilot disconcerting? Should you really be flying around by yourself if you don't know the answer to this question?

@GregTaylor Probably. As you haven't understood the question, I assume that you are a fixed wing pilot or a non-pilot and it's therefore easy to forgive the fact that your comment is arrogant, insulting and patronising. If your standard is that every pilot should know every nuance of the dynamics in narrow, theoretical (because I will never explore it) flight regimes, then the skies would be very empty. It also assumes that no pilot can ask a question about dynamics which seems a bizarre concept to me.

@Simon, sorry you feel that way, but this seems like a fundamental to me. I am a pilot, and I understand the physics of helicopter flight quite well. I'm both a fixed wing and heli pilot with PPL, and am extremely skilled in 3D RC helicopter flight (aerobatics, inverted flight, etc). Nevertheless, perhaps I do misunderstand the question.  I recommend you discuss this with an instructor before flying again, because as I said, if I understand the question, you ought to know this as a holder of a PPL

@GregTaylor You clearly haven't understood.  This is not trained or explored during PPL, nor is it covered by Prouty or Wagtendonk. I doubt that most PPLs understand it. So what leads you to believe that I should know?  Do you?  If so, why not write an answer?  And why would I discuss before I fly since you never fly into this regime and could not do so accidentally?

I guess your question is not clear. It seems the answers you've gotten explore it pretty thoroughly. To me it's no different than what happens if you pull back on the stick from a hover....you fly backward...assuming you also apply correct collective and rudder compensations. It's certainly not going to make your rotor stall, unless you are doing something very wrong.

@GregTaylor Perhaps that's the nub of your confusion.  At no point have I mentioned rotor stall.

Indeed. What other lifting surface is there on a helicopter that can stall besides the rotor blades?

@GregTaylor Do you think we can stop now and delete these comments?  It's getting really silly.  I never mentioned aerodynamic stall.  I never mentioned lifting surfaces.  You insulted me publicly and suggested that I am unfit to fly.  I will not respond again.

I'm not trying to be insulting, I genuinely do not understand what kind of stall you are talking about. If not aerodynamic stall, then what are you talking about?

If I attempt to continue maintaining the flare, attempting to come to a stop, I will sink and if I don't do anything about it, I will hit the ground. Why?

if you continue to maintain aft cyclic after the flare, you will hit the ground because some of the lift which is being generated will be used to fly the helicopter backwards, and you won't have enough power in to both maintain altitude and also maintain backwards flight (which is what you are commanding with aft cyclic). This is why we level off after the flare: to use all the lift in the vertical direction.
Its the exact opposite of take-off: if you are in a hover on the runway, and push the nose over to the 60KIAS nose-down attitude, you will descend into the runway.
Although I have never tried it, I imagine that at the peak of the flare, if I add (a lot?) of power without changing the attitude (much:), I will not descend into the runway, but rather I will start to fly backwards.

Its the exact opposite of take-off - doh! Light bulb moment.  Thank you!  That last paragraph sounds like fun.  Next time I have a CFI next to me....

As I have military pilots in my family I thought I'd ask one who has flown many helicopters in combat and S&R situations. Here is what he told me:
In normal forward flight, the disc is slanted forward, so some/majority of the thrust is downwards, but some is backwards to counteract drag or accelerate. When you decide to slow, the disc is tilted backwards so now some of the thrust is forwards.
What also happens is that the relative airflow that was impinging on the top of the disc in forward flight is now impinging on the bottom of the disc as you decelerate.
In forward flight this flow is a thrust penalty because it means that the change in downward flow through the disc by the rotor blades is more limited. I.e., the air is already flowing down and the rotor blades find it harder and harder to shove it any faster. They would need to rotate faster and faster to get any lift and then hit supersonic compressibility problems. (This is why modern blades tend to be funny shaped like Lynx/Merlin etc.)
Same problem propellers have on fixed wing. There is a speed at which they just can't propel the aircraft any faster.
Conversely, when the disc is tilted back to flare, the airflow is all bonus. It is known the rotary aviation as the green arrow and what allows autorotation.
I have zoom climbed hundreds of feet upwards whilst assaulting targets in full autorotation with the collective lever full down and essentially nor requiring engines at all.
The upshot of this is that as you transition from normal forward flight by tilting the disc back you need to lower the collective to maintain level flight or you will zoom climb.
However, you don't get something for nothing. You are trading the forward energy of the whole helicopter for rotational energy in the head.
Eventually you slow to a stop, and at this point you require engines to sustain the rotation of your rotor system, and if you have maintained a lot of nose up it is a very significant amount of power.
The power required curve for helicopters is a U shape with most power being required at hover and max speed and min at about 70kt in most helicopters.
The upshot of this is as your speed tapers off you need to steadily lower the nose or can get bitten hard by the power requirement when the forward momentum ceases especially if you are flying an underpowered toy which almost all hobby helicopters are.
This thrust deficit is exacerbated if the nose is held high because not all the thrust is supporting lift, some is accelerating you backwards.

This is an example. The pilot is coming in too hot and holds the nose very high until a very late stage. He then let's a rate of descent build and doesn't have time to arrest before hitting the ground. Hovering out of ground effect, even military aircraft don't have a lot of spare power, so it is important to correctly judge yeeha flying maneuvers and throw them away before the hover if screwing up. These guys should have thrown it away at about the moment the video starts. I have a feeling that they are approaching downwind as well which makes it all twice as bad.

This is it done properly.
He simultaneously pitches the nose up and enters auto.
You can see the relative aspect of the disc to the airflow switch from slightly downwards to very much up through the disc.
As the speed bleeds off he is progressively raising the lever to maintain height as he runs out of forward energy, then as he approaches the hover he pitches back nose down.

Thanks Rory, but sadly, this doesn't answer my question.  I know all of the above, it's just basic rotary flying and that second video is just a plain old quick stop. It's my fault, I clearly can't explain what I'm trying to understand.  Let me try it this way.  Imagine he didn't level off at the end of the quick stop, he would descend until he hit the ground, not matter how much collective he pulled.  I'm trying to understand what happens.  Is in an overpitch?  Is it rotor droop?  Do the blades stall?  The title of the question is the nub of it.

Is that not covered off by that power paragraph and the one on thrust deficit?

Because if you keep your nose pitched up, you must surely start to accelerate backwards - but that means you require much more thrust, as a good portion of it is pointed forwards. If you have enough power this is not necessarily a problem.

"You are trading the forward energy of the whole helicopter for rotational energy in the head.
Eventually you slow to a stop, and at this point you require engines to sustain the rotation of your rotor system, and if you have maintained a lot of nose up it is a very significant amount of power." < This answers the question entirely.

If you continue to hold flare attitude, and start applying power in same attitude, you will settle with power (vortex ring state). You will lose control of your helicopter and even if you yank full collective lever... you will hit ground tail down.
Worse, in case of actual power plant failure and auto recovery, if you continue to hold flare attitude.... rotor RPM will decay rapidly and you will lose control power of disc. Hence you will hit ground tail down.
Tail down attitude impact may not be safe for all helicopters, as this leads to tail rotor loss..... hence vicious yaw in powered recovery!


text:
How or when can the 250 KIAS speed limit below 10,000ft be exceeded?
This arose out of a comments discussion in this question.
The only airspace I really know is the UK.  Here, a controller may issue a clearance to exceed the 250kt limit below 10,000ft for reasons other than minimum safe flying speed, e.g. to expedite a transition for spacing.
Is this common, e.g. in the US?  I know it's open ended but I'm interested in whether this is just some "local" thing.

The German BAFVD (the controller's bible) lists that the speed restrictions can be lifted for technical reasons (aircraft limitations) and for security reasons. I queried two of my colleagues working TMA airspaces and they said that it depends on the controller when they lift the limitations. Some will keep aircraft in the protected class C and some will allow higher speeds in class E, when weather conditions do not allow VFR operations anyway. The BAFVD is not public though, so I'll leave this as a comment for you, no real answer. :/

The notion of a speed limit for airplanes raises the humorous image of a cop sitting behind a cloud with a radar detector waiting for a plane to go by... ;-)

@Michael as long as we're being silly; why bother with a cloud:  http://www.snopes.com/horrors/techno/radar.asp

@DanNeely Coincidentally a colleague sent me a copy of that text yesterday (not snopes) with the disclaimer, "probably fake".  I immediately shot back "It has to be, Sidewinders are air-to-air missiles, not air-to-ground".  We then proceeded to take apart the other flaws before finding the snopes copy.

@Michael Not only is the Sidewinder an air-to-air but it's a heat seeker.  The missile that would go after a hostile radar is a HARM.

Not a local thing at all!
In Australia, it is extremely common to hear, especially for aircraft on departure. Listening to LiveATC, particularly Sydney International Approach/Departure (YSSY) you will quite often hear ATC give an aircraft permission to exceed 250KIAS below 10,000ft.
Qantas 123:
Approach, QFA123, with you passing 2,300, climbing 5,000..
Sydney Approach:
QFA123, Identified, Climb FL240, cancel speed restrictions below 10,000..
There are a number of reasons this is used. The first, I have already hinted to in the example radio call above.
Departures:
It is extremely common to hear ATC cancel speed restrictions on departing aircraft. This gives better separation for aircraft departing in the same direction. For example, one of the busiest sectors in the world is Sydney - Melbourne Australia. The common SID's out of Sydney for Melbourne are the DEENA4 WOL transition and the WOL1 Departure, depending on operational runway. As a large amount of aircraft use these departures, the further the lead aircraft can get on the SID prior to the trailing aircraft becoming airborne, the better.
Arrivals:
Again, using Sydney, they receive a large amount of Regional Turbo-Prop traffic (Dash 8-Q300/Q400, Saab 340B, BE350). You will commonly hear Approach cancel speed restrictions on these aircraft on decent so they can give them more space on the approach. They land reasonably slower than a B747/A380, so the more room, the better.
Another reason is simple. These guys are operating commercial operations, hence faster is better, especially on descent. So if there is no or low traffic in the TMA, ATC will commonly release the speed restriction on aircraft to accommodate the company operations.

I'd forgotten about the SIDs.  In the UK, it is common to hear "no speed" meaning no restriction. If it happens in Aus, then safe to assume it's widespread. Thank you!

this answer is about Australia, but the question asks, eg. about the US

@rbp He is not directly stating it needs to be US, he is using eg. US as a way of saying not in the UK..

In the US, the 250 kt speed limit is codified in 14 CFR 91.117

§91.117   Aircraft speed.
(a) Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).
(b) Unless otherwise authorized or required by ATC, no person may operate an aircraft at or below 2,500 feet above the surface within 4 nautical miles of the primary airport of a Class C or Class D airspace area at an indicated airspeed of more than 200 knots (230 mph.). This paragraph (b) does not apply to any operations within a Class B airspace area. Such operations shall comply with paragraph (a) of this section.
(c) No person may operate an aircraft in the airspace underlying a Class B airspace area designated for an airport or in a VFR corridor designated through such a Class B airspace area, at an indicated airspeed of more than 200 knots (230 mph).
(d) If the minimum safe airspeed for any particular operation is greater than the maximum speed prescribed in this section, the aircraft may be operated at that minimum speed.

Note in section (a) that only the administrator may authorize operations below 10,000 feet MSL at speeds above 250 KIAS.  The only exception to this is part (d) which applies to aircraft that cannot safely operate below this speed.  As far as I know this only applies to specific heavy airplanes.  ATC does not have the authority to issue instructions contrary to regulation.
Historically the FAA has experimented with the ability of controllers to cancel the 250 kt speed limit within certain class B airspace, notably in the Houston, TX class B.  That program was discontinued and currently no controller may grant you an exception to the regulation.
Note that the 200 kt speed limit in class C and D surface areas and any speed restriction published on a chart (departure and arrival procedures) can be cancelled by ATC.

The military also can fly at 300kts below 10k, and often, even 350.  It can be very challenging to both descend and slow down a division of aircraft, so we often fly faster for safety.

In the US, speed restrictions are frequently cancelled, either to ensure or to increase separation between aircraft, as per ATC Handbook 4/3/14 JO 7110.65V, Section 5-7. Speed Adjustment:

5−7−1. APPLICATION Keep speed adjustments to the minimum necessary to
  achieve or maintain required or desired spacing.

Published restrictions on arrivals and departures may be cancelled, but the 250 kt limit below 10,000 MSL may not be.

@casey So what I'm hearing is that in large areas of the world (so far, I know UK and Aus), it can be cancelled, in the US not.  Is that a fair summary so far?

@casey retracted. it says Administrator, not ATC

FAR §1.1   General definitions. Administrator means the Federal Aviation Administrator or any person to whom he has delegated his authority in the matter concerned.

notably: "in the matter concerned"


text:
Why does manifold pressure increase with power?
Whilst writing an answer to this question, I remembered something I don't really understand.
The partial vacuum in the inlet manifold is caused by the piston descending with the inlet valve open during the "suck" phase of the Otto cycle.  It is this vacuum that causes fuel to be pushed into the intake, the greater the vacuum, the greater the fuel added to the inlet charge and the greater the power.
Since the needle valve is on the manifold side of the throttle butterfly along with the input to the MAP gauge, why does the manifold pressure increase with power?  I would have thought more power, more "suck", lower pressure; more pressure, less "suck", less fuel.
I'm obviously wrong since that's not how it works but why?
The answers to this question get close but I'm still missing something (and I'm sure will soon be embarrassed by the obviousness of the answer).

Possibly related: http://aviation.stackexchange.com/q/9313/167

You don't need a vacuum to draw fuel through the jet. Air passing by at speed is enough. I've got an airbrush that has a compressed air nozzle, with a paint nozzle in front. When I open the air valve, paint is drawn up from the paint nozzle into the airstream.

Manifold pressure does not actually increase with power. With a constant speed propeller when you increase rpm, the power will increase, but the manifold pressure will decrease.

@Jan Hudec, I'm pretty sure he's talking about moving the power lever, not the prop control.

@MichaelHall, when one says just ‘power’, I generally consider it to mean the actual power generated by the engine no matter how it's control levers are set. And for spark-ignition engine the usual term is ‘throttle lever’, because it controls the throttle, that term even appearing in the question.

@Jan Hudec, ok... but the way you increase the actual power generated by the engine is to advance the throttle, or power lever.  (Regardless of the prop setting)  Increasing prop RPM alone simply flattens the pitch, and as you noted, causes the manifold pressure to decrease because there is less load on the engine.  You don't increase the overall power output just by allowing the blades to spin more freely.

@MichaelHall, actually yes, you do. At higher RPM the engine will pull in, and burn, more mixture per unit of time. The manifold pressure will drop, so the increase will be less than proportional to the increase in RPM, but it will nevertheless be an increase.

@Jan Hudec, I'm not going to argue with you over nit noid details like this, but let me ask you a question:  You are leveled off in cruise flight and because of a cloud layer ahead you decide to make an easy climb of 1000' or so.  You can only touch one lever, either throttle or prop RPM.  Which one do you choose, and why?

@MichaelHall, depens; throttle has larger effect, but near the ceiling (ok, then it won't get 1000 fpm anyway) it may have nowhere to go, but RPM might.

Just curious, but are you a pilot with a complex endorsement?

And second, I said I wouldn’t argue over details, but even if the engine might pull in a bit more air at higher RPM, the power output will not increase if you don’t touch the throttle.  HP is torque multiplied by RPM, (/5252) but if you increase RPM by reducing the torque load the net output is constant.

Manifold pressure is actually a measure of the vacuum pressure between the throttle and the cylinders. The more the throttle is opened, the closer that manifold pressure returns to atmospheric pressure.
The amount of fuel provided to the engine depends on the pressure difference between the manifold and the throttle body.  The throttle body pressure will decrease as the throttle is increased, because of greater rate airflow across the venturi (faster air -> lower pressure).  The manifold pressure will increase as throttle is increased, due to the greater flow of fuel/air mix into the manifold (greater mass of air flowing into a fixed volume -> higher pressure).  So the pressure difference will get larger as the throttle is increased.
This link has a pretty good description of what's going on.

Great link. I have that printed out in my fight bag from lessons I took a while back in a DA-40.

Thanks, it is a good link.  But I still don't get (from this link or any of the answers) why reduced pressure leads to less fuel flow.  Surely it's the vacuum that draws fuel from the carb?

I think you are looking at it backwards.  It isn't reduced pressure that causes less fuel flow.  It's less fuel flow that causes the reduced pressure.  Going back to the straw analogy from below, imagine sucking on a very wide straw.  It would be difficult to create any "suck" (reduce pressure) but when the opening is narrowed, the pressure decreases (vacuum increases) ---  Looking at any fluids system can be confusing, and I'm not sure that seeing it as a cause and effect is really accurate at all.

I think this statement from the link is probably the most helpful: "Manifold pressure depends on ambient pressure, the position of the throttle plate, and the speed at which the pistons are moving up and down."
We can only directly affect one of these variables (throttle).  Increasing throttle increases RPM (with fixed pitch), but because our inlet is larger, the pressure will be raised more by the inrushing air than it is decreased by the faster "vacuum pump" action of the cylinders.

I think I've found my answer.  My mistake is in the original question.  The fuel inlet is not on the manifold side of the butterfly, it's on the intake side!  So, wider throttle setting means a reduced pressure in the intake, but an increased pressure in the manifold, which is what draws the fuel in!  With this knowledge, and the answers here, it's starting to fit together.  The straw analogy helps!  You, and @jt000, might consider editing your answers along these lines.  I don't feel they are yet complete enough to accept.  Cheers

Yeah I didn't realize how much your original question was concerned with fuel flow.  I've edited my answer to include that.

The diagrams in that link are wrong. They have the throttle butterfly upstream of the carb venturi and it is actually between the venturi and cylinder. The choke is at the position indicated, and it cannot function as a throttle.

Manifold pressure is the pressure in the fuel\air mixture between the throttle and the engine. When the throttle is at low power, then it is preventing fuel\air from flowing which causes a reduction in pressure. This is because the engine is trying to pull fuel\air, but throttle is preventing it much like sucking on a straw stuck into thick milkshake. When the throttle is wide open, then the fuel is able to freely flow & you should see normal pressure just like outside (i.e. 29.92).
In other words, the pressure is actually decreased when at low power & at "normal" pressure when at full power.
For more info check out this link

Thank you.  I'll wait to see other answers, but I respectfully think you might be wrong.  Certainly on the systems I've seen, MAP is measured in the inlet manifold and has no connection with the fuel lines.

The inlet manifold is what passes fuel\air to the cylinders. It would have to be connected to the fuel lines, wouldn't it? http://en.wikipedia.org/wiki/Inlet_manifold

No, the fuel line feeds the float chamber in the carb.  The vacuum outside the needle valve is what draws the fuel in.  The fuel line(s) does not connect with the manifold.  I've read that link and I still feel thick :)  I'm just not getting it.

Ah, now sucking on a straw in a thick milkshake is beginning to do it for me!  So as the butterfly opens, the milkshake gets thinner?  But if that's the case, why does fuel flow decrease with increased vacuum?

The engine is trying to pull fuel, but the throttle is preventing it. If there was nothing impeding fuel flow, then the pressure differential would be near 0. In cause\effect terms: cause: fuel flow is decreased, effect: pressure decreases (not the other way around).

Milkshake might not be the best example. Consider putting your finger over the straw & comparing when you finger is not on the straw. The reduced pressure that is caused with your finger on the straw is the same as low power when the throttle is blocking the fuel\air mixture.

Manifold pressure controls power production and the throttle controls manifold pressure. Pressure does not increase because more power is being made, rather, more power is made because opening the throttle (increasing pressure or reducing vacuum) allows the engine to pump and burn more fuel/air mixture.
A carburetor contains the throttle for controlling airflow into the engine. It also contains a venturi which meters the amount of fuel mixed into the air. The ratio of gasoline to air must remain approximately 14:1 in order to burn properly, so as airflow increases through the venturi vacuum in the throat also increases, pulling enough more fuel to keep the ratio correct. More fuel without more air or vice versa would cause the engine to quit.

Also shown is the choke plate, which is used to get extra fuel into a motor before it is up to operating temperature. Closing the choke adds manifold vacuum to venturi vacuum to pull more fuel into the intake. Fuel does not fully vaporize when the motor is cold and it will not burn if not vaporized, so the extra fuel makes enough vapor for the motor to run. As the motor comes up to operating temperature, the choke is opened so the normal amount of fuel is mixed with the air.

Well all pilots know that increasing throttle, or opening the throttle increases the manifold pressure so the above explanation is incomplete.  As throttle opens the induction system is open to ambient air pressure so it rises.  The volume of air is increasing and being forced into the manifold of fixed size so pressure is increasing and indicated as much on the MAP gauge. The MAP is meassured in the intake manifold not the venturi. When off the pressure throughout the induction is ambient.  But then turned on the cylinders suck air out of the manifold, but the closed throttle is choking off the air and so the MAP drops.  Then opening the throttle removes the choke and the MAP can rise up to ambient.  Or more if turbo. As more air is sucked into the manifold of fixed cross section by opening the throttle its pressure goes up.

Talk about obfuscating the issue!
Throttle plate - a variable valve to restrict air flow.
Throttle Body - a duct with a converging diverging throat. ie, a venturi. the throttle plate controls the diameter of the venturi.
Manifold - a tube connecting throttle body to cylinder.
The same air flowing through the manifold flows through the throttle body, governed by the throttle plate.
The converging shape of the venturi causes that air to speed up. the same volume of air passes through the narrow venturi, as flows through the large manifold.
As per bernoullis theorem, velocity, pressure and density are all interchangeable. the same density or mass of air flowing through a smaller duct has higher velocity, therefore lower pressure. The atmosphere then pushes fuel into the venturi/throttle body through the jet into this low area zone - The spray gun principle.
The manifold pressure shows the position of the throttle plate and how its governing air flow into engine, and therefore the power the engine will produce, the pressure differential being equal to the square of the airflow. this vacuum is completely separate to the venturi itself, which sees a pressure differential between its narrowest point and the surrounding larger duct (whether this is referenced to atmospheric pressure or not) simply due to air flowing through it having the higher velocity.
The highest manifold vacuum is actually when compression braking... especially on these fancy new efi systems with intake air control and fuel cut on decel... they can close the throttle nearly 100%... and the engine is spinning much faster than at idle...

I'm answering my own question since the existing answers are good, but do miss a key point in my question which ultimately was the source of my confusion.
I mistakenly thought that the fuel needle valve is on the manifold side of the butterfly.  Therefore, I could not understand why more vacuum (less power) did not result in more fuel (more power).
The reason is that the valve is on the intake side of the butterfly and therefore, the more open the butterfly, the lower the pressure on the intake and therefore, the more fuel.
So, increasing throttle opens the butterfly which lets more air into the engine faster, which causes a drop in pressure (because of the venturi) in the intake which draws more fuel.  Sorted!

I think you may have the misconception that power is increased by increasing just the amount of fuel. Actually, power is increased by packing more fuel/air mixture into the cylinders. The fuel/air ratio shouldn't vary all that much. Just adding more fuel would make a richer mixture, which actually decreases power.

@FredLarson Thanks, but I do get that. More air, means more fuel means bigger charge. Just increasing fuel would lead to a rich cut or overheating.  My only misunderstanding was on which side of the butterfly the fuel valve is.

Ok, good. I'll leave my comment to help anyone else who may be confused.

The intake stroke creates a vacuum in the cylinder. This vacuum allows the fuel air mixture into the cylinder.  That constant cycle keeps the manifold pressure lower than the atmospheric pressure while the engine is running.  The amount of mixture available to the cylinder is controlled by the throttle valve.  The more the valve is open the greater volume of mixture available to the cylinder.  The amount the throttle is open determines the pressure in the manifold. That is why manifold pressure is the lowest at idle and the greatest when the engine shut down.

I like to look at it like this: there is a correlation between air pressure and air velocity. When velocity is high, pressure is low. When velocity is low, pressure is high. So, when we open the throttle, we are letting more air flow into the engine. As the engine RPM increases, the velocity of the air flowing into the manifold gets higher. Internally, the pressure gets lower and this is how they are correlated. The pressure in the manifold drops as the velocity of the air increases. By knowing what the manifold pressure is related to the ambient pressure, we can tell the amount of air that is flowing into the engine. If we know the amount of air flowing into the engine, we can choose the correct fuel amount (or the computer does).

There's two vacuums that matter.  There's the vacuum beyond the throttle plate (manifold pressure) which pulls the air from the plenum, and there's the vacuum created by the venturi in the carb (venturi vacuum).  You can have high manifold pressure and still have high venturi vacuum.  The venturi is configured so that it is created by the FLOW thru the venturi, mostly independent of the pressure of the air around it.  Differential pressure (vacuum) in the venturi is created by FLOW.  Higher flow means higher venturi vacuum.  Because there is very little restriction before the throttle plate, the plenum pressure doesn't vary too much.


text:
What is the meaning of segment in MTRs?
Military Training Routes (MTRs) with no segment above 1,500' AGL shall be identified by four number characters (IR1206/VR1207)
MTRs that include one or more segments above 1,500' AGL shall be identified  with three number characters (IR206/VR207).

What is the meaning of segment in MTRs?
What is the difference between three and four?

A route is how you go from place to place.  A segment is a portion of your route which is characterized by a consistent course/altitude.
A route may have one segment, or many.  An MTR is a Military Training Route.  If no portions of the route exceed 1,500 AGL, then it is given a four-digit identifier.
I'm pretty sure that the three-digit / four-digit decision was arbitrary, but I'm ready to be educated.


text:
How can I use the "control hinge-moment coefficient due to tab" for sizing a trim tab on an elevator?
I calculated the control hinge-moment coefficient due to tab by using the dimensions of a tail and its elevator. However, the trim tab dimension parameters in the calculations were approximated values corresponding to similar aircrafts' tail geometries. Thus, what are the next steps to find the precise trim tab dimensions, and what is the role of the control hinge-moment coefficient due to tab in sizing a trim tab?
Notes:

the dimensions of the tail and elevator are precise and could not be changed
hinge-moment coefficient due to elevator is known

Since it operates in the thickest part of the boundary layer, the effectiveness of a trim tab is notoriously hard to compute. The usual procedure is just as you did: Copy what others have done before. The next step is to fine-tune the design in flight test.

The trim tab is sized first, and then the tab hinge moment is computed. The trim tab is sized to the conditions required for maximum trimmed position of the aircraft at:

low speeds;
all relevant CG positions;
all relevant flap settings;

The contribution of the trim tab to the elevator hinge moment is tiny, see the right hand graph which is measured data from the F-27.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
When did the Tu95 first use its armament in combat?
When did the Tu95 first use its armament in combat? I know they can carry both missiles and bombs, I'm looking for the earliest date of either one being used in a combat situation.

Last year (!), at least per Wikipedia:

On 17 November 2015, Tu-95s had their combat debut, being employed for the first time in long range airstrikes as part of the Russian military intervention in the Syrian Civil War.

This seems to have been using the Tu-95 as a missile platform:

The aircraft launched a total of 34 airborne cruise missiles destroying 13 key targets...


text:
Can small RC aircraft utilize a steel sheet monocoque construction?
I have seen small RC aircraft built from just about everything: cardboard, sytrofoam, fiberglass, aluminum, coroplast, etc.
Most these designs are at least partial monocoque designs. Is there any reason why sheet steel cannot be used? In comparison to aluminum, thin sheet steel is very cheap or even free. Most appliances in the US are built from approx. 1/32 inch sheet steel. It can be worked using standard tools available in a hardware store.
Are there any requirements that sheet steel would not be able to meet? I am aware that the weight-to-lift ratio of the aircraft is likely to suffer, but as long as it is capable of flight I don't consider this as much of a problem.

With a large enough engine anything will fly. Keep in mind that a steel flying machine with a large engine will probably have to fly fast to stay in the air (compared to a non-steel version of whatever you build). If you end up building this please find a very remote location for test flights. I'm picturing what amounts to an armored lawn dart filled with nitro fuel and a 1/2 horsepower blender attached to the nose.

I think your point is with a high enough performance engine, it could fly. I can't just put a J58 turbojet on my plane and expect flight.

My point is that a balsa/foam version of what you're describing may be over-powered with a .4 but a steel version will weigh considerably more and need a much more powerful engine.  I'm not saying you SHOULDN'T do it...but if you do please put a video on youtube!

Yes, it can be done, but to do it well is a lot of work. You will also need to use a thinner gauge than 1/32" to get the weight down.
Note that one of the very first all-metal aircraft was made of 0.2 mm (1/128") sheet steel and flew well. However, building it required a corrugated substructure and a welded steel tube frame for strength. Still, it was heavier than necessary so its builder switched to aluminium for later designs.
Generally, the tension length of steel (strength relative to density) is roughly equal with that of aluminium or titanium; however, you will need to use high-grade steel to be comparable with aircraft-grade aluminium, so some of the price advantage will be lost.
But there is a distinct disadvantage with higher-density materials. While their strength scales linearly with wall thickness, their buckling strength scales with the square of their thickness. You will end up with a very delicate structure which will require careful handling to avoid local dimples and a stiff substructure to avoid early failure in compression. Also, introducing loads locally (say, for a landing gear or an engine mount) will require local reinforcements which should ideally be multi-layered and taper out in several steps.
If you want to scale an existing structure down, make sure you place the stiffeners closer than what a scale construction would require. But I am sure you will prefer to bond the sheet steel to a styrofoam core. Use a higher-density styrofoam with better compression strength and be generous with local reinforcements, and the model should turn out fine.

Note that the 1/128" sheet aircraft is a full-sized aircraft. For a "small" RC plane (by RC standards, "small" is typically 1m or less wingspan or fuselage length) you'd need steel sheets thinner than tissue paper - so thin that you can probably weld it with a lighter and it would most likely be impossible to touch (kind of like planes built with nitrate microfilms which melt on touch)

@slebetman Based on the feedback in answers, perhaps the real answer is a steel fuselage with a more traditional wing structure.


text:
Can I land on an abandoned runway in California?
Can a private pilot land on an abandoned runway in southern California's remote areas?
There are a few unpaved runways near scenic hillsides, ideal for camping or swimming.

Who owns the land the runways are on?

I guess federal parks, or some public agency. One of them is Lake Arrowhead airport.

We have some related questions on the site, e.g. here, here. The short answer is that the FAA regulates what happens in the air, not on the ground, so you need the landowner's permission to land or take off.

Are those runways actually abandoned?  Or are they just backcountry strips that get little maintenance?

Don't forget this other question: Will you be allowed to takeoff from there without a safety team, an instructor, and prior to a NTSB investigation?

As noted in the comments it depends on who owns the land and what the local regulations are. With permission and proper operations it may be ok.
However if the runway was formerly active and is now no longer maintained its likely a bad idea to try and land on it. The FAA can even get you under their catch all 91.13 Careless or reckless operation.
There are procedures for closing a runway and marking it as such (you can find the AC here). Some times the "x" used to mark the closure is a physical structure that can make it dangerous to land on the runway. In other cases the runway may no longer be suitable for use or there may be active construction going on. While the runway may appear to be ok on the surface that does not mean it is safe to land.


text:
How does setting takeoff flaps improve aircraft performance?
A study guide I recently found indicates that Vmc and aircraft performance improve with takeoff flaps set. The Vmc improvement makes sense but the performance improvement does not. At a basic level, drag = bad and flaps add drag...a lot of drag.
The question is, "how does aircraft performance improve with takeoff flaps set?"
The Airplane Flying Handbook (FAA-H-8083-3B) page 12-17 indicates that takeoff flaps will degrade aircraft performance:

If flaps were used for takeoff, the engine failure situation becomes
  even more critical due to the additional drag incurred.

See also FAR 23.149.

What "performance" are you talking about? Take-off performance (distance) may improve, while fuel performance may decline...

"Performance" in the context of the other factors of Vmc.  This seems to be measured as rate of climb

Rate of climb at a given speed may improve or not, depending on where on the drag polars you operate. Generally, when normal, flap-dependent speeds are flown, field performance improves while climb performance reduces with increasing flap setting.

Right, but at Vmc do flaps improve or degrade performance?  The guidance I'm digging up indicate that performance degrades.  This makes sense and the study materials that I've seen are incorrect.

I really don't think you're asking about Visual Meteorological Conditions here... but by all means feel free to roll back if you are. :-)

Nope.  Not VMC, but Vmc.

... does your question state which configurations are compared here? Performance improves with takeoff flaps e.g. when compared with landing flaps.

Good point.  Versus clean.

Closely related, maybe a dupe?

No, that question is procedure.  This is Vmc.

Can you reference the source, or go back to it and look what exactly does it mean by performance? (It can't be maximum rate of climb, because flaps quite surely decrease that; it is possible that they increase the maximum angle of climb if the conditions are just right though).

I think the term "takeoff performance" in that context means takeoff distance and departure gradient for obstacle clearance.  Obviously, takeoff distance is shorter with takeoff flap than without.  And a departure with takeoff flap will generally, depending on the airplane, have a steeper gradient than without, even though the total climb rate is degraded with takeoff flap out.  On an IFR departure, or a regular airplane clearing trees at the end of the runway for that matter where you fly at best angle instead of best rate, gradient is the key performance factor, not so much rate of climb.
Transport aircraft generally don't start to accelerate to retract flaps at least until reaching 1000 ft agl, to keep the initial climb segment as steep as possible. Some noise abatement procedures for airliners require keeping takeoff flap deployed beyond the normal retraction schedule, typically to 3000 feet instead of 1000 feet.  This is to keep the climb as steep as possible to a higher altitude so as not to upset unusually sensitive neighbours farther away from the airport.
That sort of thing is a luxury that jets enjoy because of the massive power reserves. Not so much in a piston twin, which has very little performance reserve when single engine and loaded.  Where an AFM says to do so, you would want to avoid climbing with takeoff flap any more than you have to for obstacle clearance, since if an engine quits, the airplane's climb gradient becomes more of a descent gradient until flaps and gear are retracted, and even then what climb you get is pretty stately - and only if your speed and technique is spot on.
So I don't think the seemingly contradictory conditions you gave are inconsistent in that context.

I do not know if/when aircraft will have a better climb gradient with flaps ( in fact I suspect they don’t), but to retract the flaps the plane will now have to accelerate to a higher speed. This ensures a flatter gradient, not necesarely an aerodynamic fact of flaps, but using the engines to accelerate rather than climb

FAR 23.149 doesn't mention takeoff performance specifically (nor does the question). I think "performance" of a GA piston twin, in this case, relates to an airplane's ability to climb, hold altitude, or achieve minimum possible sink. While an engine may fail on takeoff, Vmc certification rules do not require obstacle clearance guarantees or any minimum climb rate.

My answer is (as in most cases): It depends. Mostly on the type of flap used and the position defined as zero.
Camber flaps
Camber flaps do not necessarily increase drag, at least at moderate deflection angles. Maybe it helps to think of an unflapped wing as of one where the flaps have been permanently fixed in one setting. And this setting does not necessarily need to be the one which offers minimum drag. Changing the setting of chamber flaps shifts the optimum angle of attack range up or down without changing drag much - until you reach extreme flap settings where the contour break is too big to be left unnoticed by the airflow.

The plot (made with XFOIL 5.4; own work) shows how the laminar bucket is shifted up and down the c$_L$ range without affecting drag much except for the -20° setting - here, the suction peak on the lower side in combination with the strong flap camber is too much for the boundary layer to remain attached. But this setting is really useable for inverted flight only.
Setting flaps to a slightly positive angle does indeed increase performance:

The maximum lift coefficient is higher, allowing lower lift-off speed and a shorter ground run.
The maximum climb angle is increased greatly especially for propeller aircraft as the aircraft can climb at a lower speed where thrust is higher for the same engine performance. Note that the polar point for maximum climb angle sits at a high lift coefficient, especially for a wing with high aspect ratio. Therefore, positive flaps might be required to operate the aircraft at its best climb angle speed safely.
Maximum sustained turn rate is also helped greatly with moderate flaps. The plot below shows calculated turn radii for a large unmanned reconnaissance aircraft at several rates of climb (or descent). The line for 0 m/s is the stationary turn rate.

Turn rate diagram for two flap settings: 0° (blue lines) and +10° (red lines). Own work.
Several fighter aircraft used flaps effectively to maximize their turn rate in dogfights (google for "combat flaps"). Also, the living wing concept of the F-18 adjusts flaps to maximize wing performance in all situations. This would not help if flaps only reduce take-off runs.
Fowler flaps
These flaps increase wing area, so here any actuation will also increase the friction drag coefficient, since that is referred to the wing area with retracted flaps. However, since the increased wing area allows to fly more slowly, the total drag might be lower, depending where on the polar the aircraft flew before extending flaps. A moderate take-off setting will, therefore, also result in reduced drag if the aircraft is able to fly more slowly and induced drag is less than half of total drag.
At full deflection, fowler flap drag grows out of proportion to lift, but that is one of the design goals. The higher settings are meant for landing only.

Flaps do indeed increase drag.
They also increase lift.
The reason flaps are used for takeoff is that the increased lift allows the aircraft to become airborne at a lower speed (which reduces the amount of runway needed for taking off) and - up to a point - climb more steeply for a given speed (which increases obstacle clearance after taking off).  The downside of flaps is that the increased drag requires more power from the engine(s) in order to maintain speed; sans engines, or sans some of a multiengine aircraft's engines, the aircraft's airspeed airbleeds off more quickly with flaps than without, due to said increase in drag (this is aggravated by the increase in lift, which makes the plane want to go up - trading airspeed for altitude - more than it otherwise would), which makes you sink more steeply and come down shorter than you would with flaps retracted.

„climb more steeply for a given speed“ is not quite correct, I believe - there is a best angle-of-climb speed for any given flap, and extending more flap than that for which the current speed is optimum speed will most probably decrease performance, not increase it...?

@CptReynolds: You are correct (edited to clarify), but it's still better than no flaps at the speeds in question here.

I appreciate the contribution.  This seems to be a description of what flaps do and why they are used though.

It reduces Vmc in the same way that having the landing gear extended does ie by creating a ‘keel effect’  with an increased induced drag behind the CG and moving the CL more aft on the chord line.  This will increase longitudinal stability and reduce the minimum control speed.  Also flaps set to the AFM’s approach or takeoff setting increase lift with only a modest increase in drag.  Check with what the manufacturer recommends here.

I have no problem with that concept. The Vmc improvement makes sense. The guide indicates that Vmc improves and performance improves. I want to understand how the performance improves. I'm starting to think it's just an error. The question is aircraft agnostic.


text:
Is there a standard format for pre-departure clearances?
I am curious to know, from current airline pilots, if the formatting - and therefore reliability and ease of use - of pre-departure clearances (PDC's) has improved since they were first introduced?
Back then we would see differing formats, incorrect flight numbers and routings, and the like.  ATC would send them to the company and then the company would give them to the flight crew together with other relevant documents.
I'm sure that the process has greatly improved since those days, but I'd like to know if PDCs have now been standardized?

I know nothing about PDCs, but it does seem that they are now standardized. One aircrew training site said in April 2014:

For those of you capable of receiving a Predeparture Clearance (PDC),
  have you noticed a change since the first week of April? The FAA
  changed the way it issues PDCs. Gone are the days of trying to decide
  if you got a reroute in the PDC. The FAA recognized there was a
  problem with standardization with regards to reroutes

The article points to JO 7110.113, Procedures for Issuing Automated Clearances, which says:

5. Explanation of Policy Changes. This order is revised to provide standardization of PDC clearances across the FAA.

I guess you can read the rest of the JO for more information, it means nothing to me :-)


text:
Does airspeed impact fuel flow?
Let's say an F-104 Starfighter is flying at sea level at 600 KIAS with throttle at 100% RPM.
Then, let's say the F-104 is still flying at sea level, but the pilot reduces throttle and airspeed falls to 250 KIAS. The pilot then pushes the throttle to 100% RPM and starts accelerating.
My question is, at 100% RPM, will fuel consumption be greater at 250 KIAS and less at 600 KIAS?
Does airspeed impact fuel consumption? The higher the airspeed, the less fuel consumption, and the lower the airspeed the greater the fuel consumption?
note: I added this chart after I made this post:

Perhaps you should frame it in terms of ram air effect on specific fuel consumption (lbs fuel per lb thrust per hr).  Thrust declines with speed initially, until ram effect with airspeed starts to provide a "compression boost" and net thrust goes up.  To the extent that net thrust goes up, FF should also go up so the answer is probably airspeed increases fuel consumption to the extent that it is increasing net thrust in the speed region you're talking about. Unless SFC is going down due to efficiency increases from ram effect, so maybe FF doesn't go up. I have no idea if that is the case.

John,
Let's say a fighter produces 10,000 lbs of thrust at sea level. When the fighter is flying at, say, 250 KIAS, it might be only producing, say, 8,000 lbs of thrust at that airspeed? And then when speed increases to, say, 500 KIAS, it would be producing 10,000 lbs of thrust?

John, See the chart I added to the post. It shows thrust variation with airspeed.

You need to check the method of fuel injection in the Starfighter.  If it only has to do with throttle setting and nothing else, airspeed is not a factor, it will dump in a given amount of fuel for a given throttle setting.  But I would imagine, even with a plane that old, a primitive computer compensates for air flow/ram pressure.  The linear increase of "lb m/hr/lb fuel" graph of the turbo jet seems to show "my drag squares but my speed doubles".

I don’t believe that airspeed directly affects fuel flow, but it may impact other variables that can have an influence.
I don’t have a flight manual for an F-104, but for the EA-6B the manual says the following about the fuel control unit on the J52P-408A engine: (straight turbo jet, non-after burning, 1970s technology)

“The engine fuel control is divided into a computing and metering
section.  The computing section monitors throttle position, burner
pressure, engine speed, and compressor inlet temperature.  These data
are translated into a fuel demand that is relayed to the metering
section, which measure the correct amount of fuel from the engine fuel
pump the fuel pressurizing and dump valve.”

Of those four inputs the primary would be throttle position, with metering occurring to dampen out pilot inputs and ensure smooth operation.  The other three may be influenced by environmental conditions such as airspeed, altitude, etc. but airspeed itself is not an input.
Modern FADEC, (Full Authority Digital Engine Control) engines might be different.

So it sounds like that engine used compressor rpm instead of EPR as an indication of power?  Was there an EPR indicator?

@John K, correct, no EPR.  But I really didn’t use RPM as an indicator of power.  RPM was for when I introduced fuel on start, checking at idle, then again at max blast to make sure the limit wasn’t exceeded.  All other times I’d just set power for a target airspeed or fuel flow.  RPM was largely supplementary info in flight.

It would appear to be yes.  See Page 22 of this paper by the Hamburg University of Applied Science.  In the chart (below) on Page 22 of representative engines, the turbojet's Thrust Specific Fuel Consumption increases from .8 lb/hr/lbs thrust at 0 airspeed to about 1.0 at Mach.  So the engine is most efficient from a SFC perspective while stationary and efficiency declines with speed.  Then, when you allow for the potential for the higher speed to increase the net thrust available, the fuel burn goes up just from the increase in energy conversion, on top of the reduced efficiency in doing that conversion.

So John, if a pilot is flying a fighter at sea level at 100% MIL power, and he is flying at 300 KIAS, he will see his PPH gauge increase and increase as his airspeed keeps increasing?

I would expect so as net thrust would be going up at some point so more fuel required to make it, plus efficiency would be declining as TSFC goes up with speed which would require more fuel even if you kept the net thrust value constant.


text:
How A330-200 or 243 would be much safer under the ETOPS terms?
I am flying this week to France in an Airbus A330-200. I have a phobia of flying I have several questions here on the aviation forum. The plane is A330-200 is the one we're going with and I am reading about it. It works under the term ETOPS.
I read this part and now I am scared more than ever and I didn't understand it correctly:

In aviation vernacular, the colloquial backronym is "Engines Turn Or
  Passengers Swim", referring to the inevitable emergency water landing
  of a twin engine aircraft after a double engine failure over water
  outside gliding range of land. But ETOPS operation has no direct
  correlation to water or distance over water. It refers to flight times
  between diversion airports, regardless as to whether such fields are
  separated by water or land.

The company I am flying with, its fleet has an average age of 5.6 years in 2016, making MEA one of the youngest fleets in the world.

I edited the question.

Air travel is safer (statistically) than the car you are traveling in to get to the airport. So don't be afraid.

I think the wording is overly dramatic and I understand that this would be alarming to someone with a phobia. The linked answers explain ETOPS well but the paragraph you cited refers to a hypothetical situation where a twin-engine jet loses both engines. The point of ETOPS is to certify that any aircraft flying far away from land never experiences such a failure. As far as I know, none ever have.

@Hugh, I know one and one that came close (over water, there were more over land). And notably, having more engines would not have helped, because it was common cause. Still there was maybe 50 all-engine failures through all history (on airliners). Way less risk than car accident on the way to airport indeed.

And what about the gear is not down while landing ? Like the polish airplane

@Hugh  I can think of at least BA9, which wouldn't have been able to make it to land, and TS236, which made it to land.

@ChristianLee any links about the both incidents ?

ETOPS (Extended Twin Operations - at least that’s what it used to be called) is a set of rules comprising of flight planning, flight operations, aircraft maintenance, flight training and administrative procedures which are geared towards making aircraft operations safe in those regions where diversion airfields are not easily found, e.g. when crossing large oceans.
When these rules are obeyed (i.e. when operating under ETOPS), that should make flying very safe.


text:
Why do we often have more than one method of slowing down (retarding) aircraft on the ground?
Why do we often have more than (thrust reversers and brake chute) one method of slowing down (retarding) aircraft on the ground?

I'm not sure your question has enough detail @Heisenberg. Do you mean thrust reversers and brakes, or something else?

Because the effect is cumulative... I agree with @GdD, there is not enough detail here, you need to explain what you mean, I could just pull the power back and it will slow down, or use brakes, or use aerodynamic braking, etc...

@GdD thrust reversers and brake chute

This seems very similar to this question, although I don't know if it's really a dupe

Yet some aircraft have no means of slowing themselves at all. The friction of rolling across the ground or the tailskid dragging along is sufficient.

@TomMcW which aircraft would that be?

@HarshilSharma Older taildraggers like the Tiger Moth had no brakes. They were designed to land on dirt or grass runways which gave enough rolling friction to stop them.

The multiple methods of braking help to stop an aircraft faster, both through providing different means of braking and complementing each other.
The wheel brakes are the primary method of braking on the aircraft. They work at any speed and can provide good braking force depending on the amount of friction between the tires and ground. Brakes convert the aircraft's kinetic energy into heat, and have a limited ability to dissipate that heat. Aircraft may be delayed from taking off to allow brakes to cool down after a rejected takeoff or a short turnaround. Brakes wear down over time and must be replaced. Aircraft that are light and slow may be fine with only wheel brakes, as the other methods are less effective in this case and would add complexity and weight.
Speed brakes or spoilers usually extend from the top surface of the wing. This both increases drag and reduces the lift produced by the wings, and are most effective at higher speeds. Reduced lift means more weight on the wheels, increasing their friction and the effectiveness of brakes. Airliners will typically extend the spoilers immediately after touchdown to increase braking and control effectiveness as they slow down. Aircraft are required to be able to demonstrate a rejected takeoff and stop using only brakes and spoilers on a dry runway. Techniques such as keeping the nose high as long as possible or just holding up elevator can also add aerodynamic braking.
Reverse thrust redirects some of the engine's thrust forward. This provides a braking force and for engines under the wing also helps interrupt airflow over the wing, reducing lift. Jet engines redirect core and/or fan air forward, propellers may change pitch to push the air forward. This can be particularly important on contaminated runways were low friction limits the effectiveness of the brakes. Reverse thrust is generally only used at higher speeds to reduce the risk the debris or exhaust being ingested.
These are the primary methods available on airliners. Brakes are the most versatile but require friction and must be replaced. Speed brakes and reverse thrust use aerodynamic forces at higher speeds to help slow down, and increase effectiveness of brakes. Speed brakes are basically "free", reverse thrust is relatively cheap and effective. Reducing the load placed on wheel brakes reduces temperature and wear; steel brakes deteriorate much more at higher temperatures. Having multiple methods provides some redundancy as well, but when runway friction is poor it's important that they are all used effectively to stop the aircraft.
Drag chutes are another option to slow down. Upon landing, the parachute is released and uses drag to slow an aircraft down. The parachute provides large amounts of drag but must be collected and re-packed after every landing. This is useful for aircraft with high landing speeds where cost is less of an issue, such as fighter jets or the space shuttle.
Tail hooks grab cables on the ground, and the cable provides the braking force to the aircraft. This can stop the aircraft quickly but requires an aircraft designed with a hook that can withstand the braking forces. Hooks are useful on aircraft carriers where space is at a premium, but this requires pilot skill to touch down in the right place for the hook to catch the cable. Hooks can also be used on regular runways for emergencies, where the extended hook will catch the cable as the aircraft rolls past.

Thrust reversal can also be used to make an airplane move backwards, which is handy when waiting for a tow truck might take too long.
On some types of aircraft, e.g. the C-130, thrust reversal can be used to start another aircraft, by parking them nose to nose.

I would suspect that it is due to redundance, safety and usefulness in different circumstances.

Thrust reversers are useful to slow down from high speeds, but you wouldn't want to use them when trying to stop at a gate.
Wheel brakes are powerful both at high speed and when parking, but can catch fire if the temperature resulting from the braking gets too high. Also less efficient on slippery runways.
Some (primarily) military aircraft have tailhooks despite not being designed to land on aircraft carriers. The hooks provide an alternative to ejecting and loosing an otherwise good aircraft if the systems powering the brakes fail.
Braking chutes are as far as I know mainly used on aircraft without thrust reversers; these provide an alternative to wheel brakes which is useful in certain parts of the world. Norwegian F-16 and F-35 are equipped with braking chutes as they regularly operate in areas with lots of ice and snow. Braking chutes must be jettisoned before taxiing, and has to be repacked before they can be used again, so they are less common than the other methods.

There are probably other means of slowing down I've forgotten to list. If you are on an aircraft with only one means of slowing down, what do you do when it doesn't work? Having multiple means to slow down means that any passengers or crew has a higher chance of surviving, and also that a failure can result in less damage to the aircraft.

Air brakes are another method of slowing, but obviously less effective as the speed drops

Agreed! Definitely for redundancy. I've seen plenty of planes with stuck thrust reversers, all we do is manually close them on the ground and lock out tag out the controls. Pilots then have to go a little heavy on the breaks next time.

When an airplane first lands it will be close to flying speed, the wings will still be producing lift which will keep pressure off the main wheels, making wheel brakes much less effective. Thrust reversers, speed brakes and braking chutes are designed to slow airplanes down until the wheel brakes can be used. They also reduce the landing distance needed, so runways can be shorter.


text:
How is the direction of the hydraulic fluid changed so that the cylinders and pistons can move backwards and forwards?
How is the direction of the hydraulic fluid changed, so that components and actuators (cylinders and pistons) can move backwards and forwards?

Aircraft use hydraulic systems, but not really sure this is aircraft related.

This is really a very basic mechanical engineering question.

Using hydraulic valves.

Take a look at How Do Hydraulic Cylinders Work?

The fluid direction does not change, there is a valve that either directs fluid to the extension side of the piston, or the retraction side of the piston. The "non-pressure" side of the piston is also directed back to the tank so that there isn't (much) back-pressure on the other side of the piston.

I agree the question is not aviation specific but I would argue to keep the question here as I don't know if there is some specififcity for aircraft's hydraulic systems (perhaps speed or reliability constraints)

The direction of travel is controlled by a directional control valve for a double acting cylinder.

The red line is high pressure from hydraulic pump. when the high pressure fluid is entering the right chamber and push the actuator piston to left.
The low pressure fluid in left chamber (blue line) will leave the actuator and return to reservoir.
If we rotated/move the directional control valve clockwise it will look like the figure below :

The high pressure will enter the left chamber and move the actuator piston to right

Downvoted as it clearly need editing efforts before reaching quality standard as defined in the help center

@ManuH got edited, see if you want to rethink your vote

I agree ilustration improve the answer's quality, but it still lack editing efforts. e.g. the first sentence is not a sentence.

@ManuH Then edit it?

Great diagrams!


text:
Could wingsuits replace or supplement ejection seats?
I know that ejection seats are good to help save pilots' lives, but they're not foolproof either and the design hasn't changed for decades.
Why don't pilots wear a squirrel suit or wingsuit so that they can fly away to open the parachute far from the enemy?

A wing suit has a glide ratio of only 2.5:1 in ideal conditions. That's no more than 20kms of horizontal flight, which means that you're not likely to reach any safe place.
Ejecting from a fighter jet is not an ideal condition. The odds of being knocked out be the blast, canopy or whatever made you abandon your aircraft in the first place are very real. Furthermore, ejection at very low altitude is not unheard of. This is why the chute is not deployed manually, and why the chute is not controllable like skydiving 'mattresses'. You don't want to tumble out of control!
Finally, you're carrying a small raft and some emergency supplies, all of which would not improve your glide slope. The jet is really the best method of reaching a safe place; ejecting is only there to reach the ground with most limbs attached if your supersonic get-the-hell-out-of-here vehicle is compromised.

"ejection at very low altitude is not unheard of." Excellent point. I would go so far as to say ejection at low altitude is probably the norm. Most of the time the pilot is fighting to recover or at least try to avoid people on the ground. Ejection comes a second or two before impact. Not sure a wingsuit would even have time to establish any lift at 50-100 feet.

I agree. 0-0 seats weren't developed because the engineers got bored. There was and is a need for them.

Apart every possible aerodynamic consideration, wearing a wingsuit in the tiny space of a cockpit would be extremely difficult.
In the F-16, for instance, there are instruments, switches and the ejection seat handle between the pilot legs (source: Wikimedia):

Limited arms' movement is another issue. Having parts of the suit randomly catching switches, levers, etc. will be a safety nightmare.
Also, many fighter jet's don't have explosive bolts that release the canopy during ejection, but rather some cordite in the glass to break it during the ejection sequence, like the AV-8B Harrier II (source: www.b-domke.de):

Passing through a shattered glass with the aforementioned wingsuit could tear off some part or lead to injuries to the pilot.

I assume you mean a wingsuit.
The idea behind ejection seats is that in a fighter jet, you are seating on tons of explosive materials (Jet fuel, munitions, ...).
You want to get away from that as quickly as possible.
A wingsuit would be very inconfortable to wear in the cockpit during nominal flight, and it would be almost impossible to get off of the plane at high speed without ramming it, probably killing yourself in the process.
=> Ejection seat is the only solution for high speed/potentially explosive bail out.
Sail plane on the other hand don't explode and fly relatively slowly so jumping away with a parachute is doable.
You might ask why not using ejection seat THEN wingsuit
It would be impractical as it would only gives you very limited range (strikes can be done hundreds or thousands of kilometers inside hostile zone.
And the ejection seat is so brutal that you would probably not be able to maneuver it properly after the shock of the ejection.

Also, the seat contains a survival kit for sea and land.

No, it is a 3 stage process.  The concept would be to convert the seat chassis itself into some type of guided flying platform like a rocket jet suit.
1) The ejection process and auto parachute deploy would be the same as now.
2) Next after deployment the pilot while parachuting down has an option to just parachute down. OR if over hostile territory to further deploy a jet pack that separated from the seat and chute, and the pilot could fly away some distance.
3) There would be a secondary parachute that could be deployed miles away after flying the seat (jetpack).

Please watch your language in your posts.

More specifically, StackExchange has a general policy of "be nice" that applies to all posts. For more information about what's expected on SE sites, please see [answer] and the [help].


text:
Can the thrust reversers still be activated if the landing gear won't extend?
In the case of Boeings, I understand that the thrust reversers cannot be activated unless the landing gear is extended.
However, would it still be possible to activate the thrust reversers if the landing gear cannot be extended due to a technical malfunction, and the aircraft has to belly land? Would it be helpful to activate thrust reversal in this scenario?

No, not helpful. Before touchdown you want a shallow approach, and after touchdown the braking will take care of itself. No need for thrust reversers.